Re: PKG_CHECK_MODULES on system without pkg-config installed?

[Jef Driesen]

On 10/03/11 17:14, Dave Hart wrote:
> On Thu, Mar 10, 2011 at 1:53 PM, Jef Driesen<address@hidden>  wrote:
> > You don't have to convince me of the advantages of using pkg-config.
> > I want to use pkg-config for exactly the same reasons as you explain.
> > But when I tried to build my project on a system without pkg-config
> > installed it failed. Proceeding without the feature (that would be enabled
> > through the pkg-config checks) would be perfectly acceptable, except
> > that autoconf fails on the PKG_* macros and aborts. So I can't build
> > anything at all and that's the main problem.
>
> I actually didn't use the PKG_ macros at all so I didn't run into this
> problem -- configure.ac searches for pkg-config using AC_PATH_TOOL and
> invokes it.
>
> However, I like the idea of using PKG_* m4 macros instead, and I'm
> disappointed to hear of your snag.  Do not despair, you can use the
> macros on systems that have them (and not break on systems without) by
> using m4_ifdef to conditionalize the use.  For example, this is how
> ntp-dev enables Automake's silent rules generation without requiring
> automake 1.11, which was the first release to provide AM_SILENT_RULES:
>
> m4_ifdef(
>      [AM_SILENT_RULES],
>      [AM_SILENT_RULES([yes])]
> )

I noticed there are projects (see for example [1]) that ship the pkg.m4 file, 
and then add this line in configure.ac:

AC_CONFIG_MACRO_DIR([m4])

and in the toplevel Makefile.am:

ACLOCAL_AMFLAGS = -I m4

I haven't tried this yet, but I assume it works. But I wonder what happens on a 
system that does have pkg-config installed. Does it use the system wide pkg.m4 
file or the local one? If it's the local one, then the downside is that you have 
to keep this file up-to-data. But other than that it looks like the best option.

[1] 
http://mailman.videolan.org/pipermail/libbluray-devel/2011-February/000232.html